Not Applicable.
Not Applicable.
1. Field of the Invention
This invention relates to methods of ultrasonic inspection of long-distance pipelines, mainly trunk oil pipelines, oil-products pipelines and gas pipelines, while providing acoustic communication between the ultrasonic sensors and the pipe walls (for example, with the help a so-called xe2x80x9cpigxe2x80x9d or a scanning device which is put into the pipeline and transported under power of the fluid flow in the pipeline). The inspection pig has built-in sensors, means for measurement, conversion and recording of the measured data and a device for collecting the digital data in the process of pig travel and for processing the obtained data to detect the flaws in the pipe walls and to determine the parameters of the detected flaws, as well as their location in the pipeline.
2. Description of the Related Art
Known in the art is a method of in-tube ultrasonic inspection [RU2042946, RU2108569, U.S. Pat. No. 4,162,635] effected by passing inside a pipeline a scanning pig having ultrasonic sensors, measuring means for measurement, processing and storage of the measured data. During the pig travel ultrasonic probing pulses are emitted towards the walls and the respective reflected ultrasonic pulses are received.
Also known in the art is a method of in-tube ultrasonic inspection [WO96/13720 (relevant patent documents: U.S. Pat. No. 5,587,534, CA2179902, EP0741866, AU4234596, JP3058352), EP0304053, (relevant patent documents: U.S. Pat. No. 4,964,059, CA1292306, NO304398, JP1050903), U.S. Pat. No. 5,062,300 (relevant patent documents: CA1301299, EP0318387, DE3864497, FR2623626, JP2002923), U.S. Pat. No. 5,460,046, (relevant patent documents: EP0684446, JP7318336), EP0271670 (relevant patent documents: U.S. Pat. No. 4,909,091, CA1303722, DE3638936, NO302322, JP63221240), EP0616692, (relevant patent documents: WO9312420 U.S. Pat. No. 5,635,645, CA2125565, DE4141123, JP2695702)] by passing inside the pipeline a scanning pig accommodating ultrasonic sensors, means for measurement, processing and storage of the measured data, and by emitting ultrasonic probing pulses during the pig travel and receiving the ultrasonic pulses reflected from the internal and external walls of the pipeline, the run time of the above pulses being measured.
These methods allow one to find out corrosive flaws such as loss of metal and scaling and to determine the parameters of these flaws. However, to detect crack-like damage of the pipe wall and to determine their depth, one needs information on the amplitudes of the received pulses. The absence of such an information in the above methods does not allow one to use these methods for crack detection.
Known in the art is a method of in-tube ultrasonic inspection of pipelines [RU2018817] effected by passing inside the pipeline a scanning pig carrying ultrasonic sensors, means for measurement, processing and storage of the measured data, emission of ultrasonic probing pulses during the pig travel and reception of the reflected ultrasonic pulses corresponding to the probing pulses with the help of said ultrasonic sensors, amplifying the output electric pulses of the sensors corresponding to the received ultrasonic pulses, converting and storing the measured data.
This method is characterized in that a mirror ultrasonic pulse is separated from the received ultrasonic pulses depending on the arrival time, the electric pulses corresponding to the separated mirror ultrasonic pulses are converted into a control voltage depending on the amplitude of the mirror pulse, and the control voltage is used to control the amplification of the pulses reflected from the flaws.
An advantage of this method is that it allows one to correct the errors when measuring the amplitudes of the pulses arising due to the acoustic attenuation in the depositions on the inner wall of the pipeline, the thickness of these depositions being different in the different sections of the pipeline.
The main disadvantage of the above method is that the method is practically inapplicable for reception of ultrasonic pulses subjected to multiple reflections because it is practically impossible to separate xe2x80x9con-linexe2x80x9d mirror pulses with preset parameters among all repeatedly reflected ultrasonic pulses for generating a control voltage. Besides, in the given method no account is taken for the attenuation of the ultrasonic pulses in the pipe wall and the losses due to the partial penetrability of the media interface during the multiple reflections in the pipe wall.
The prior art of the proposed invention is a method of in-tube ultrasonic inspection of pipelines [U.S. Pat. No. 5,497,661 (relevant patent documents: WO9210746, EP0561867, CA2098480 DE4040190)] by passing inside the pipeline a scanning pig comprising ultrasonic sensors, means for measurement, processing and storage of the measured data, including the steps of emission of ultrasonic probing pulses during the pig travel and reception of the reflected ultrasonic pulses corresponding to the probing pulses, using the same ultrasonic sensors, amplification of the electric pulses from the sensors, corresponding to the received ultrasonic pulses, conversion and storage of the measured data.
This method is characterized in that it includes reception of at least one ultrasonic pulse reflected from the inner wall of the pipeline and at least two ultrasonic pulses reflected from the external wall of the pipeline, the reflected pulses being picked up by at least one ultrasonic sensor and amplified.
To receive the pulses after emitting the probing pulse, a time window is created having such a width that the pulse reflected from the inner wall of the pipeline and the two pulses reflected from the external wall of the pipeline are within the window, the received pulses being digitized.
The digitized pulses are filtered and parametrized. The maximum time and amplitude are determined for each reflected pulse and compared with a digital threshold value.
The width and amplitude of the reflected filtered and parametrized pulses are sent to a computer module, in which the parametrized pulses are processed to determine the time between the arrival of the nearest pulse reflected from the external wall of the pipeline and the arrival of the pulse reflected from the inner wall thereof. The parametrized pulse whose amplitude is higher than or equal to the amplitude of the previous pulse is recorded.
The time of the pulse generation and the time of its run in the pipe wall are determined and recorded if the time slot between the ultrasonic pulse reflected from the pipeline inner wall and the first pulse reflected from the pipeline external wall coincides within an allowable limit with the time slot between the first and second pulses reflected from the external wall of the pipeline. In so doing all parametrized pulses, for which said time slots do not coincide within the allowable limit are recorded.
In this method both the time from the moment of emission of the probing pulse to the moment of reception of the reflected pulses and the amplitude of the reflected pulses are measured and this is a necessary condition for detection of cracks in the pipe wall. However, the crack detection is effected using ultrasonic pulses emitted at some angle (about 17xc2x0) to the normal of the inner wall of the pipeline and reflected from the crack forming a corner reflector with the internal or external wall of the pipeline. In this case, a crack-like flaw corresponds to one reflected ultrasonic pulse, and the application in the prior art condition of coincidence of the time slots between the multiple reflected pulses is inefficient. Besides, the amplitudes of the multiple reflected ultrasonic pulses decrease depending on the total thickness of the metal layer penetrated by the pulse and on the amount of reflections from the media interfaces.
An advantage of the prior art method is that the digital threshold value is varied depending on the result of selection of the pulses on the basis of a preset threshold value. However, for all reflected pulses corresponding to one ultrasonic probing pulse only one digital threshold value is set, i.e. a single threshold value for pulses with different amplitudes during the time of reception of the pulses corresponding to one probing pulse. As a results, the preset threshold value is undervalued for the first pulse (with a high amplitude) and is overvalued for the last pulse (with a low amplitude).
Furthermore, when testing a pipeline including pipes with a different wall thickness, the flaws having the width correspond to the pulses with different maximum amplitudes, the obtained data on the flaw width and, respectively, on its danger is unreliable.
Thus, there is a need for an improved method of in-tube ultrasonic inspection of pipelines.
A method according to the invention for in-tube ultrasonic inspection of pipelines can also be realized by passing inside the pipeline a scanning pig having ultrasonic sensors, means for measurement, processing and storage of the measured data; during the pig travel said method provides emission of ultrasonic probing pulses and reception of the reflected ultrasonic pulses corresponding to said probing pulses with the help of said ultrasonic sensors; amplification of the electric pulses fed from the sensors and corresponding to the received ultrasonic pulses; conversion and storage of the measured data; the amplitudes of the received electric pulses corresponding to the reflected ultrasonic pulses are compared with a preset threshold value, the time elapsed from the moment of emission of the ultrasonic probing pulse being determined in the process of measurement.
The present method differs from prior art methods in that within a selected time interval the amplification of the electric pulses from the ultrasonic sensors and the threshold value are varied discretely as preset functions of time, the dependencies of the amplifications factors and threshold values on time are read out during the scanning pig travel inside the pipeline from the device of conversion and storage of digital data while establishing individual dependence of the amplification factor and threshold value on time for each sensor simultaneously when the ultrasonic pulses are being received by this sensor.
The basic technical result obtained due to the realization of the invention is better probability of detection of flaws, especially crack-like flaws, when testing the pipelines including pipes having essentially different thickness of the walls and/or different properties of the pipe material, and a higher accuracy of determining the flaw size.
The mechanisms of achievement of this technical result consists in that a time-depending control of the amplification factor allows one to use the maximum accessible range of the analog-to-digital conversion (ADC) both for the pulses having passed a low thickness in the wall (at a small number of reflections or in a thin-walled pipe) and for the pulses having passed a larger thickness in the wall (at a great number of reflections or a thick-walled pipe) and to adjust the digital threshold value depending on the number of multiple reflections of the ultrasonic pulse and taking into account the periodic increase of the noise level depending on time elapsed from the moment of emission of the probing pulse.
In the process of searching crack-like flaws, the method allows one to use hardware to normalize the amplitude of the electric pulses corresponding to reflected ultrasonic pulses. The normalized amplitude of the ultrasonic pulses reflected from the crack-like flaws, to some extent, unambiguously corresponds to the depth of the crack or another flaw, and such hardware normalization allows one to realize the algorithms of the express analysis of the danger of the flaws under field conditions after completing the pig travel.
The amplification factor is discretely varied with a period of 2 to 20 microseconds and at a maximum step of 0.25 of the initial value of the amplification factor.
The threshold value is set up discretely with a period of 1 to 10 microseconds.
The lower limit of the above time interval is 3-20 microseconds and the upper limit of the interval is 40-200 microseconds.
The realization of the present method allows one to organize digital control of the dependence of the amplification factor and threshold value on time arbitrarily both before starting the scanning pig and during the pig travel inside the pipeline. The method can also be used for determining damage such as loss of metal by recording the multiple reflected ultrasonic pulses, as well as for detecting crack-like flaws.
The amplification factor K of the electric pulses from the ultrasonic sensors is increased depending on the time t elapsed from the moment of emission of the ultrasonic probing pulse, according to the function K=c+a*(t-b)n with a positive value xe2x80x9caxe2x80x9d, a value xe2x80x9cnxe2x80x9d not less than 1 and value xe2x80x9cbxe2x80x9d not exceeding the above-mentioned lower limit of the time interval; c is any appropriate value. In the preferred embodiment of the method, n=2.
In another embodiment, the amplification factor K of the electric pulses from the ultrasonic sensors is increased stepwise depending on the time elapsed from the moment of emission of the ultrasonic probing pulse characterized by the number of the step M, maximum number of steps N, and the initial value of the amplification factor K0 according to the function K=K0*(1+a*2Mxe2x88x92N) with a positive value xe2x80x9caxe2x80x9d and a value xe2x80x9cNxe2x80x9d not less than 6. In the preferred embodiment of the method, N=8.
The above dependencies approximate empirical dependence for the attenuation of the ultrasound energy in medium being transported, deposits, material of the pipe wall in the working time interval of reception of ultrasonic pulses.
The amplification factor is controlled by periodically varying the noise level of the electronic circuits depending on time. The variation of the threshold value depending on time allows one to control the conditions of recording the received reflected ultrasonic pulses for each instant of time separately.
The dependence of the threshold value on time is set as a function of number of false pulses for some preset time interval exceeding the preset threshold value.
The false pulses are noise pulses.
Owing to the fact that the plurality of pipes constituting the pipeline being tested can include a considerable number of pipes made of a material whose acoustical absorption properties differ from those of the other pipes, and that the noise level of the electronic channels is a parameter depending both on the type of the ultrasonic sensors and on the individual properties of the sensors of the same type, the preliminarily selected dependence of threshold value on time is corrected depending on the efficiency of reducing the amount of data to be recorded. Such a progressive approximation allows one to adjust the efficiency of recording the useful pulses (corresponding to the reflected ultrasonic pulses) by preset criteria.
The false pulses are presented both by noise pulses and ultrasonic pulses reflected from the structural elements of the pig housings and sensor holders. As the number of such reflected pulses is low, the interpretation of the data effected after completing the scanning pig run enables the operator to uniquely identify such pulses.
The dependence of the threshold value on time is established in such a way that one probing pulse corresponds to 8-16 received false pulses exceeding the threshold value.
The application of the present method has shown that the above criteria are optimum for preventing the loss of useful pulses below the threshold and for avoiding overload of the electronics by processing the false pulses.
In one of the embodiments of the method, the number of false pulses, determined after completing the pipeline inspection by the pig, the dependence of the threshold value on time is set up for the subsequent diagnostic pig travel.
The analysis of the efficiency of application of thresholds for different sections of the main pipeline allows one to separate the effect of variation of the parameters of the electronics and a change of the type of pipes at different sections in the process of motion of the pig in the pipeline and to apply the most effective dependence for the subsequent diagnostic pig travel through the pipeline.
The above mentioned time interval is divided into some temporary zones, the scheme of division into temporary zones is used after each probing pulse, the false pulses are counted up in each zone, the threshold value for each zone is set depending on the number of false pulses exceeding the threshold in the respective zone for several probing pulses. A preferred number of temporary zones is not less than 4 and not more than 128. The temporary zones provide adjustment of the temporary dependence of threshold. A low number of zones provides coarse adjustment of the threshold. A large number of zones (fine division) allows one to adjust the threshold more precisely depending on time. The maximum amount of temporary zones is limited by the pulse duration.
The dependencies of the amplification factor and threshold value are established depending on the fluid medium being transported, when testing the pipeline, the passed distance and the pipe wall thickness. The initial values of the amplification factor are determined for each ultrasonic sensor before emitting the ultrasonic pulses to the wall of the tested pipeline by triggering the ultrasonic sensor by an electric pulse with preset parameters, thus forcing the sensor to emit an ultrasonic pulse perpendicularly to the nearest surface of an object of a known thickness and by receiving a respective ultrasonic pulse reflected from the remote surface of the object with the help of the same ultrasonic sensor while varying the amplification factor according to the algorithm realized by the data conversion and storage means to obtain a pulse with a maximum amplitude of the pulse. The code corresponding to the initial value of the amplification factor determined in this way is recorded in the digital data conversion and storage device. The lower limit of this range is at least 0.7 maximum allowable amplitude of the pulse, the upper limit being 0.8 maximum allowable amplitude of the pulse. In the present method, the digitized amplitude values of the received electric pulses are compared to the digital threshold value. The realization of the above algorithm allows automatic determination of the initial values of the amplification factor immediately before starting the scanning pig and during the pig travel (with metering the pipeline thickness).
In the preferred embodiment of the method, the amplitude of the noise pulse is measured at the absence of the probing and reflected ultrasonic pulses; the range of the analog-to-digital conversion of the amplitude values of the electric pulses corresponding to the received ultrasonic pulses are set as a function of the measured amplitude of the noise pulse; the amplified electric pulses corresponding to the received ultrasonic pulses are applied to one of the inputs of an adder; from the adder output the pulses are applied to the input of an analog-to-digital converter, and applied to the second input of the adder is a voltage from the digital-to-analog converter, said voltage depending on the measured amplitude of the noise pulse; another voltage is applied to the second input of the adder through a low-pass filter, the range limits are set depending on the number of discrete values; the range limits are set depending on the noise pulse level.
These operations allow one to use the maximum range of the ADC by removing the pulses corresponding to the noise of the electronic channels from the analog-to-digital converter.
The digitized parameters of the received pulses (corresponding to the probing pulses for each ultrasonic sensor are combined into data frames (for a group of sensors); The above parameters of the received pulses include digitized amplitudes of the pulses and time elapsed after emitting the respective probing pulse for each peak value. In the preferred embodiment, the alternative parameters of the received pulses include digitized peak amplitudes of the pulses and the time corresponding to the peak amplitude after emitting the respective probing pulse. An embodiment is preferable, in which one of the data frame includes the above parameters of the received pulses corresponding to 10-1000 probing pulses for each sensor of the group of ultrasonic sensors, for each said group of sensors a value of time is recorded, which is determined by a timer installed in the scanning pig, this time being uniquely matched with the time of triggering each sensor of the group. The digital data are recorded in the digital data storage device as a file of a plurality (100-10000) of data frames, as well as the time of opening and closing the file according to the clock of the computer controlling the data storage in a storage device. The computer clock time and the timer time are synchronized with each other and with the time of another timer located beyond the scanning pig. The above form of data recording allows one to uniquely determine the time of measurement of the data in case of distortion of some data in the process of conversion, recording, storage or reading and to find the reason of any malfunction.
These and other features, aspects, and advantages of the present invention will become better understood upon consideration of the following detailed description, drawings, and appended claims.